1. Field of the Invention
This invention relates to semiconductor devices and, in particular, III-V semiconductor devices.
2. Art Background
Devices, e.g., light emitting diodes (LEDs) and lasers based on III-V semiconductor materials, generally are fabricated on a bulk semiconductor substrate such as a bulk indium phosphide substrate. A typical fabrication step involves the epitaxial deposition of a III-V semiconductor material on the heated substrate through the thermally induced reaction in a gas mixture at the substrate surface. A variety of deposition mixtures has been employed. One class of mixtures suitable for the deposition of III-V semiconductor materials containing phosphorus are those including phosphine as the source of this phosphorus. Thus, for example, for the deposition of indium phosphide, the initial gas mixture includes phosphine as a source of phosphorus and indium chloride as a source of indium.
The morphological quality of the deposited layer significantly affects device quality. A common defect in the growth of III-V based semiconductor materials by hydride epitaxy is the formation of hillocks, i.e., crystallographic defects including a portion of grown material that extends at least 0.5 .mu.m above all other grown material within an area of 100 .mu.m.sup.2. (See G. H. Olsen, GaInAsP Alloy Semiconductors, edited by T. P. Pearsall, John Wiley & Sons, page 11 (1982) for a description of hydride epitaxy, i.e., an epitaxial process where the source of the Group V element is phosphine, and the walls of the reactor in the reaction region of the apparatus are heated by an external source such as a furnace). Hillocks, however, substantially degrade or catastrophically limit device properties such as current confinement, light output, electrical contact performance, and reliability. Additionally, hillocks often preclude device fabrication steps, such as contact mask pattern delineation, which depend on a planar morphology. In an attempt to limit morphological defects such as hillocks, growth on substrate surfaces that are slightly misoriented, e.g., 1 to 6 degrees misoriented from a crystallographic plane such as the (100) plane, has been attempted. Despite this precaution, substantial hillock formation still occurs. Additionally, for many structures whose fabrication depends on the use of precise crystallographic orientation, even the slight improvement attained by misorientation is precluded. For example, in the fabrication of V-groove lasers, the production of the groove depends on the in-plane crystallographic orientation of the substrate. If a misoriented substrate is utilized, an unacceptable etch structure such as a dovetail, rather than a V-groove, is obtained. Thus, hillock formation remains a significant source of degradation in device yield and efficacy.